1. Field of the Invention
This invention relates to the treatment of crystalline aluminosilicate compositions, especially crystalline aluminosilicate zeolites, with an ionic source of chromium whereby alumina is caused to be removed from the aluminosilicate composition. More particularly, this invention is directed to increasing the sorption capacity and the pore diameter of porous crystalline aluminosilicate zeolites having ordered three-dimensional networks of pores and channels by removal of alumina from the zeolite. This invention is further directed to incorporating a form of chromium into the zeolite in a non-ionic form where it can function, under appropriate conditions, as an oxidation catalyst. Thus, the invention is directed to a method of alumina removal, the resultant compositions and hydrocarbon conversion with the resultant compositions, especially cracking and oxidation.
2. Discussion of the Prior Art
Crystalline aluminosilicates have been contacted previously with sources of chromium. Thus, it is known to contact a zeolite with a solution of a chromium salt for purposes of ion exchange. U.S. Pat. No. 3,232,762 discloses room temperature ion exchange of the sodium form of zeolite Y employing an aqueous solution of CrCl.sub.3.6H.sub.2 O. The final water washed material, pursuant to an example, contained 9.9 weight percent Cr.sub.2 O.sub.3 (or 6.7 weight percent chromium) and 2.9 weight percent Na.sub.2 O. These data indicate that the chromium chloride treatment of the zeolite is an ion exchange, chromium for sodium.
The Russian workers N. F. Ermolenko and L. V. Pansevich-Kolyada (Materialy Vses. Soveshch. po Tseolitam, 2nd, Leningrad 1964, pub. 1965, 171-178) reported that a zeolite A was prepared with alumina replaced by Cr.sub.2 O.sub.3 via an ion exchange of chromium for aluminum. The method of Ermolenko et al. differs greatly from that of the present invention in that zeolite A has a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of only 1.85 .+-. 0.5 (U.S. Pat. No. 2,882,243) and the treatment temperature was 110.degree.C. The present invention requires that the SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio be greater than 3 to about 12 for the very important reason that when said ratio is 3 or less, and an acidic medium is used, i.e., one having a pH of less than 3.5 as in the present invention, the crystal structure is destroyed. The object of the method of the present invention is to maintain the crystallinity under the conditions employed for the subsequent benefits rendered thereby.
The Russians (L. V. Pansevich-Kolyada et al.) again reported (Vesti Akad. Navuk Belarus. SSR. Ser. Khim. Navuk, 1970, (1), 85-89) that they prepared Cr.sup.+.sup.3 - containing zeolite A, X, Y and M by ion exchange of the zeolite with 0.01N chromium acetate solution. Only minimal exchange was obtained and, when the concentration of chromium acetate was increased, the crystal structures were destroyed (Note that zeolite X has a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of 2.5 .+-. 0.5, U.S. Pat. No. 2,882,244, and zeolite M has a ratio of 2.1 .+-. 0.1, U.S. Pat. No. 2,995,423). Although zeolite Y has a SiO.sub.2 /Al.sub.2 O.sub.3 mole ratio of between 3 and 6, their treatment conditions are different from those required in the present invention for effective removal, as opposed to exchange, of alumina (exemplified in Example 18 hereinafter).
In U.S. Pat. No. 3,459,815, there is disclosed a method of ion exchange of montmorillonite clay with a chromium salt. The ratio of chromium to aluminum in the patent method is less than 0.5, whereas said ratio required by the method of the present invention is greater than 0.5.
It is known, therefore, that zeolites generally can be treated with a source of chromium. However, the prior art has not revealed a method whereby a source of chromium can be used to substantially increase the sorption capacity of porous crystalline aluminosilicates by removal of substantial quantities of alumina as in the present invention. Moreover, not only is the alumina removed, but chromium is placed within the composition in a nonionic manner where it is available to function as an oxidation component. Treatment of crystalline aluminosilicates with a chromium salt of a mineral acid has heretofore, in the absence of the critical process parameters herein required, only provided ionically exchanged zeolites with no significant alumina removal while maintaining a substantially crystalline structure.